Mechanical lapping mechanism of nanotwinned cubic boron nitride

Abstract

In order to manufacture a nanotwinned cubic boron nitride (nt-cBN) cutting tool which is promising to cutting ferrous metal, especially for hardened steel, lapping mechanism is investigated with both theoretical and experimental methods. The dynamic critical lapping depth of nt-cBN is first calculated by theoretical analysis, and then proved through lapping experiments. Based on the critical depth, nt-cBN bulk is lapped in ductile regime and fine surface can be achieved. Moreover, aiming to reveal generation mechanism of the plastic grooves on lapped surface, both depth and width of the grooves are studied according to theoretical calculation and experimental results. It indicates that the dynamic critical lapping depth of nt-cBN is 23.9 nm, and surface roughness of lapped nt-cBN with 0.5 μm diamond grits is 1.99 nm and PV value is 77.05 nm. Additionally, the theoretical minimum groove depth on fine finished nt-cBN surface is 2.25 nm which was proved by experimental results, as well as the grooves' width in sub-micron scale is generated under the complicated reaction of free grits and fixed grits. Therefore, nt-cBN material has excellent machinability as compared to diamond, and can be machined by mechanical lapping with high efficiency and high precision.